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Synthesis and crystal structure of K2U2O7and Mössbauer (237Np) studies of K2Np2O7and CaNpO4

Authors
Journal
Journal of the Less Common Metals
0022-5088
Publisher
Elsevier
Publication Date
Volume
139
Issue
2
Identifiers
DOI: 10.1016/0022-5088(88)90016-1

Abstract

Abstract K 2U 2O 7 single crystals have been synthesized from a melt containing uranium, niobium oxides and potassium carbonate. The crystal structure of K 2U 2O 7 has been determined (space group R 3 ̄ m , a = 3.96(2) A ̊ , c = 19.82(4) A ̊ , Z = 3 2 ). This study led to three possible distributions for the oxygen vacancies: on the uranyl bond, on the oxygen atoms of the equatorial plane of the uranyl polyhedron or on both of these two sites. A Mössbauer ( 237Np) study of the isotypic compound K 2Np 2O 7 showed that the vacancies are located on the oxygen positions in the equatorial plane of the neptunyl ion. Mössbauer spectra of CaNpO 4 have been recorded at 4.2 K and 77 K. The isomeric shift value for this compound has been attributed to a neptunium(VI) ion with a coordination number of eight.

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